It's spring. Which means inevitably that wherever you are, someone will be asking jovially what it is about sunny days that means everyone gets more attractive. We're sick of this conversation. So here's why.

After careful scientific analysis, we think that fairly simple factors are behind individuals or groups that seem hotter at a fleeting glance in March than December. Especially in a city like New York.

More people: It's a nice day. Most street corners do not feature a miserable battle for cabs. You're walking around more. Everyone else is walking around more. You're all doing it at a more leisurely pace. There will inevitably be more street-based interactions, verbal and non-verbal, with other people. See also…

Eye contact: When it's cold, windy, snowy or rainy your head will naturally be down. It's the best way to protect your face, with its associated seeing, hearing, tasting smelling and breathing holes. When it's sunny your head is more often up. You're looking around. So is everyone else. Eye contact. I think she likes me. ‘Why are there so many hot girls around today?'

Better moods: You're in a better mood, perhaps even more confident, because you're not leaping over slushy puddles. The same applies to other people who are not leaping over slushy puddles. Everyone feels more attractive. So they look... perkier.

Sunglasses: Literally and figuratively cover a multitude of sins. Firstly, people do not pick sunglasses in which they look bad – a lot of thought has gone into those Hepburn knockoffs. Secondly, the kids these days wear large shades. These cover more of the face in case of busted-ness.

More skin: We are, at base, simple animals with simple needs. Many of us have not seen cleavage, or a toned biceps in three or four months. We've been judging people almost exclusively, in body terms, by how well their coats and sweaters fit. Obviously the first instance of exposed flesh is going to ring the dust off the attractiveness bell. The thought of that flesh will, at a passing glance, distract from any facial sins that more dispassionate scrutiny might reveal.

Memetics: As a critical mass of people talk about how they see more hot people walking around on sunny days, others listen and seek out further evidence to support the theory. If an illicit government group removed all attractive people from the streets on sunny days, it would still take a couple of years for the memetic momentum to die away. We see more attractive people on the streets on sunny days because we assume we will.